<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>案例-轮播图</title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    ul,
    ol,
    li {
      list-style: none;
    }

    img {
      width: 100%;
      height: 100%;
      display: block;
    }

    .banner {
      width: 100%;
      height: 500px;
      position: relative;
      margin: 50px 0;
    }

    .banner>ul {
      width: 100%;
      height: 100%;
      position: relative;
    }

    .banner>ul>li {
      width: 100%;
      height: 100%;
      position: absolute;
      left: 0;
      top: 0;

      opacity: 0;
      transition: opacity .5s linear;
    }

    .banner>ul>li.active {
      opacity: 1;
    }

    .banner>ol {
      width: 200px;
      height: 30px;
      position: absolute;
      left: 30px;
      bottom: 30px;
      background-color: rgba(0, 0, 0, .5);

      display: flex;
      justify-content: space-around;
      align-items: center;
      border-radius: 15px;
    }

    .banner>ol>li {
      width: 20px;
      height: 20px;
      background-color: #fff;
      border-radius: 50%;
    }

    .banner>ol>li.active {
      background-color: orange;
    }

    .banner>div {
      width: 40px;
      height: 60px;
      position: absolute;
      top: 50%;
      transform: translateY(-50%);
      background-color: rgba(0, 0, 0, .5);
      display: flex;
      justify-content: center;
      align-items: center;
      font-size: 30px;
      color: #fff;
    }

    .banner>div.left {
      left: 0;
    }

    .banner>div.right {
      right: 0;
    }
  </style>
</head>

<body>
  <div class="banner">
    <!-- 图片区域 -->
    <ul class="imgBox">
      <li class="active"><img src="./轮播图imgs/01.jpg" alt=""></li>
      <li><img src="./轮播图imgs/02.jpg" alt=""></li>
      <li><img src="./轮播图imgs/03.jpg" alt=""></li>
      <li><img src="./轮播图imgs/04.jpg" alt=""></li>
    </ul>
    <!-- 焦点区域 -->
    <ol>
      <li date-i="0" data-name="point" class="active"></li>
      <li date-i="1" data-name="point"></li>
      <li date-i="2" data-name="point"></li>
      <li date-i="3" data-name="point"></li>
    </ol>
    <!-- 左右切换按钮 -->
    <div class="left">&lt;</div>
    <div class="right">&gt;</div>
  </div>
  <script>
    //获取到所有承载图片li和所有承载焦点的li
    var imgs = document.querySelectorAll('ul>li')
    var points = document.querySelectorAll('ol>li')
    var banner = document.querySelector('.banner')

    //准备一个变量，表示当前是第几张，默认是0，因为默认显示的是索引第0张
    var index = 0

    //书写一个切换一张的函数
    //约定：
    //参数为true，我们切换下一张
    //参数为false，我们切换上一张
    //参数为数字，我们切换到指定索引的那一张
    function changeOne(type) {
      //让当前这一张消失
      imgs[index].className = ''
      points[index].className = ''

      //2.根据type传递来的参数，来切换index的值
      if (type === true) {
        index++
      } else if (type === false) {
        index--
      } else {
        index = type
      }
      //判定一下index的边界值
      if (index >= imgs.length) {
        index = 0
      }
      if (index < 0) {
        index = imgs.length - 1
      }
      //让改变后的这一张显示出来
      imgs[index].className = 'active'
      points[index].className = 'active'
    }

    //给轮播图区域盒子绑定点击事件
    banner.onclick = function (e) {
      // console.log('点击事件')

      //判断点击的是左按钮
      if (e.target.className === 'left') {
        console.log('点击的是左按钮')
        //切换上一张，调用changeOne 方法传递参数为false
        changeOne(false)
      }

      //判断点击的是右按钮
      if (e.target.className === 'right') {
        console.log('点击的是右按钮')
        //切换下一张，调用changeOne 方法传递参数为true
        changeOne(true)
      }

      //判断点击的是焦点盒子
      //dateset就是date-开头的自定义属性专门设置
      if (e.target.dataset.name === 'point') {
        console.log('点击的是焦点盒子')
        //拿到自己身上记录的索引
        var i = e.target.getAttribute('date-i')
        //切换某一张，调用changeOne 方法传递参数为要切换的索引
        changeOne(i)
      }
    }

    //自动切换功能（间隔定时器）
    setInterval(function () {
      //切换下一张
      changeOne(true)
    }, 5000) //1000ms=1s
  </script>
</body>

</html>